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Menu: Membrane

This menu is active only in the states of Analysis and Patterning. In Form finding, it is not necessary at all since we are not materializing anything in this state.

Edit

When you click this menu, a window opens up with the data of the membrane used in the structure. WinTess3 allows you to work with a single membrane at the same time. Thus, if the structure is composed by more than one module, all of them must use the same membrane.

In this window we have:

  • Name of the membrane
    We choose from a drop-down list which is connected with the database of the membranes.
  • Resistence (daN/5cm)
    This value can be a single datum (250) or double data separated by a slash with no internal spaces (300/280). These values correspond to the resistance to the breaking load of the membrane in any direction (single datum) or differentiating the resistance in the direction of the warp and weft (double data for warp/weft).
  • Modulus of elasticity (t/m) (10kN/m)
    It can be single or double with the same criteria discussed in the case of resistance.
  • Diagonal elasticity  (t/m) (10kN/m)
    This value is significant only if there are diagonal bars. In other cases, it is redundant.
  • Weight (kg/m²)
    Weight of 1 m² membrane in kg.
  • Safety factor
    This value reduces the membrane resistance in any direction. It is usually not a value recommended by manufacturers or by regulation in general. However, widely used value is 5 for the majority of permanent membranes and a little smaller values for temporary membranes. To modify this value the program goes to the window of safety factors.
  • Prestress (%) (Warp/Weft)
    With this value, we introduce a prestress in the membrane. If you have bars defined as membrane type (1) with the distinction of whether they are warp or weft, the applied prestressing is made according to this.
    The prestressing assumes that the membrane has been made smaller, in proportion to the value entered, and that then at installation we stretch it to the initial form that we have used in the project by prestressing of cables, edges, etc.

A large button to “save this membrane into the database“. If the user has manipulated and modified values of the membrane, it is possible to add this “new membrane” into the data base. Most probably it will be necessary to modify its name.

At the bottom of the window, we see a box with a series of numerical data, related to the membrane and its pre-stress.

Ferrari Fluotop T2 1202
Rk = 560/560 daN/5cm = 11200.0 kg/m
Rd = Rk / 5 = 112 daN/5cm = 2240 kg/m

Prestress
(Warp/Weft) = 0.5/0.5 %
= 16.25 / 16.25 daN/5cm
= 325 / 325 kg/m
= 2.9% / 2.9% Resist.

The first line is the name of the membrane. Then the value of the breaking strength Rk of membrane warp/weft in units daN/5cm and kg/m. On the next line, the same thing but with the resistance for Analysis (having applied the safety factor).

At the bottom, if you entered a value of prestress, we see the effect of this prestress, as always in the direction of the warp/weft:
1) in percent (%)
2) tension (daN/5cm)
3) tension (kg/m)
4) in proportion to the break resistance of the membrane (%)


Swap Warp/Weft

By clicking this menu all warp membrane bars change to weft bars and vice-versa.


Remove membrane

By clicking this menu all membrane bars (warp, weft or diagonals) are eliminated. This allows the user to analyse a structure supposing that the membrane has disappeared or has been broken, so we can check if the remaining structure is able to stand up.
To better understand it, please read blog entry: Redundancy.


Database

In the database, we save the mechanical properties of the membranes used in structures. This issue has been introduced in another paragraph Objects|Membrane.

Clicking on this menu opens database file in text format.

If we want to make a backup of this file, we can locate it in the folder shown in the title of the window.
It is important to carefully modify this file, so there are no mistakes that could invalidate the entry and affect the program. If it happens, it is better to delete the file and WinTess3 will generate another again with the basic membranes.

membrane-database2

To modify or edit this database, we must keep the following information in mind:

  • Resistance. This value can be a single datum (250) or a double data separated by a slash without internal spaces (300/280). These values correspond to the break resistance of the membrane in either direction (single datum) or differentiating the resistance in the directions of warp and weft (double data warp/weft).
    The units are daN/5 cm.
  • Membrane weight. Units in kg/m².
  • Modulus of elasticity. You can enter a single value, double or triple, with the same approach as that has been used in the case of the resistance. However in this case it supports a triple value (90/80/40) where the third value is the modulus of elasticity of the membrane in the direction of 45º with respect to the warp or the weft.
    The units are t/m = 10 kN/m
  • Membrane name. Whatever the user wishes, except that there can not be blank spaces in the name. If you want to use blanks in the database, they should be in the “¬” symbol. So a name such as “ETFE¬200¬micras” is equivalent to “ETFE 200 microns” in WinTess3.

Create a new membrane

This menu is very similar to the edit menu. To define a new membrane we must enter:

  1. Its name
  2. Its resistance (breaking load)  Warp/Weft
  3. Modulus of elasticity (see blog entry)
  4. Diagonal elasticity
  5. Weight

Finally we save this membrane into the data base. If another membrane exists with the same name, we’ll get a warning message and nothing will be saved.